The present invention relates to electrolyzers and in particular to electrode structures for electrolyzers. The invention also relates to a method for electrolyzing water, through the use of a preferred electrolyzer apparatus.
The technology of producing hydrogen by the electrolysis of water dates back to the last century. Generally, the process has been accomplished by placing electrodes into a water solution containing electrolyte material, often potassium hydroxide or hydrochloric acid. When an appropriate electrical current is passed through the electrodes, by applying an electric potential between them, oxygen bubbles form at one electrode and hydrogen bubbles form at the other. The gases may then be collected, purified and used.
Commercial electrolysis equipment, utilizing this technology, has been available for many years. A recent development in the area has been the substitution of a solid polymer type membrane material between the two electrodes, making possible the electrolysis of substantially pure water, i.e. water without substantial electrolytes added. This is advantageous since it yields more efficient conversion and generally includes lower cell maintenance cost. A solid polymer electrolyte also provides the capability of producing hydrogen at relatively high pressure, thereby at least partially eliminating the need for potentially expensive and energy intensive secondary compressors.
Solid polymer electrolytes (SPE) are well known and have been described in the following publications:
"Solid Electrolytes Offer Route to Hydrogen", Chemical and Engineering News, Aug. 27, 1973; "Electrolytic Hydrogen Fuel Production With Solid Polymer Electrolyte Technology"; Tigterinton, W. A. and Fickett, A. P.; VIII IECEC Proceedings; and "A Hydrogen-Energy System", published by American Gas Association, 1973. As indicated by these references, an SPE is typically a solid plastic sheet of perfluorinated sulfonic acid polymer which, when saturated with water, becomes an excellent ionic conductor. The ionic conductivity apparently results from the great mobility of ions, for movement through the polymer sheet, by passing from one sulfonic acid group to another. An anode and cathode are positioned on either side of the sheet, and are generally pressed thereagainst to form the desired SPE cell.
Electrolysis devices utilizing such an SPE cell are described in U.S. Pat. Nos. 4,056,452 and 4,210,511. In these devices, the anode plates have, on at least one of their sides, alternating ridges and grooves. This generally makes the anode plates costly, since the grooves are relatively expensive to fabricate.
Further, as for example in the electrolyzer of U.S. Pat. No. 4,210,511, these conventional systems have required back-up rings for supporting outer seal members that are used to seal the outer perimeter of the cathodes and to prevent escape of water containing hydrogen therefrom. Typically, the back-up rings have been machined from fiberglass or similar materials and have thus been relatively expensive.
With such conventional electrolyzers or electrolyzing apparatus, there have been problems with rupturing during use, sometimes causing severe damage to the cell and substantial downtime. In particular, pressure within the cell may cause rupturing of the relatively expensive back-up rings. In addition, usually very tight tolerances must be used in such conventional cells, especially in the fabrication of the back-up rings, in order to achieve proper sealing. When a large diameter cell is desired, these tight tolerances will tend to make the back-up rings one of the more expensive parts of the cell.